1. Field of the Invention
The present invention relates generally to a constant velocity universal joint for automotive vehicles and, more particularly, to the constant velocity universal joint used in an automobile propeller shaft.
2. Description of the Prior Art
The constant velocity universal joint for automotive vehicles, particularly the constant velocity universal joint used on an automobile propeller shaft when in use rotates at a high speed and does therefore require a capability of rotating in a balanced state and, also, a capability of suppressing internal heat generation. To attain a good rotatory balance, a gap present inside the universal joint has to be minimized in size. However, the smaller the gap, the more considerable generation of heat, and therefore in order to suppress the heat generation, the frictional resistance occurring between mating component parts must be reduced by minimizing surface roughness of those component parts. For this reason, in the constant velocity universal joint of a fixed ball type, contact surfaces of an inner race, an outer race and a cage all forming parts of the universal joint are, after those component parts have been heat treated, machined to secure a required dimensional accuracy and a required surface roughness. Also, as a means for reducing the frictional resistance inside the constant velocity universal joint, formation of a coating of a solid lubricating agent on those component parts is known in the art such as disclosed in, for example, the Japanese Laid-open Utility Model Publication No. 2-121333.
The grinding process generally requires a relatively long machining time as compared with the cutting process. Also, the grinding process requires the use of a coolant of a kind which is offensive to the environment.